Move close enough to allow Franklin on board. With fast driving skills, Franklin can board the boat just as Michael exits the tunnel.

After Franklin jumps aboard the boat, keep on the boat's tail and then start shooting at the baddies when Franklin gives the word. Press the L1/LT button to do drive-by shooting from the front window. When the coast is clear, Jimmy will end up dangling on the mast.

For this requirement, Michael needs to catch Jimmy in ONE try. As soon as Jimmy is seen dangling from the sail, get in close to the waypoint and wait for him to drop. Make sure the road is clear so that you don't have to slam on the brakes!

For PS4/X1/PC versions, you'll need to switch to Third-Person view, otherwise you may not be able to catch Jimmy within the time limit if using First-Person view.

With Jimmy safe in the car, drive in close to the boat and catch Franklin. Get in close and a quick cutscene shows Franklin jumping off the boat to the car hood. From there, the engine gives out, so make a U-turn and drive to LS Customs to make some repairs.

After the cutscene, drive in to LS Customs and get the car fixed free of charge. Now that the car is fixed, drive it back to Michael's house.